Generally, thermoplastic resins are molded and used as base materials for vehicle interior and exterior materials. Among them, polypropylene (PP) resin is mainly used since it is excellent in physical properties to a price and also has a melting temperature of 150 to 160° C., which is suitable for bonding with other materials and for performing heating and molding process. However, there are some disadvantages that the polypropylene resin has poor heat-resistance so that it is contracted by heat, and has weak strength at a low temperature such as the winter season so that it breaks or ruptures.
For overcoming such disadvantages, conventionally additives such as wood powder and calcium carbonate have been mixed with the polypropylene resin, alternatively, glass fiber reinforced thermoplastics (GMT), which is a mixture of polypropylene resin and glass fiber, has been applied to various applications. However, the additive mixing method could not fundamentally solve the above disadvantages.
FIGS. 1 and 2 show processes of producing a thermoplastic material according to the conventional art. As shown in FIGS. 1 and 2, in case of glass fiber reinforced thermoplastics (GMT), the polypropylene resin 1 and the glass fiber 2b are supplied together to the extruder 5 so that the length of the glass fiber 2 should be about 10 mm. For this, first, the glass fiber 2a from the roving yarn 2 is fed to a fiber cutter 4 through a fiber moving tube 3 to be cut to about 10 mm. Next, the polypropylene resin 1 and the glass fiber 2b which is cut are supplied to the extruder 5 at the same time to be melted and extruded from the extruder 5, and then pressed by a press roller (calender) 6. The pressed material is hauled off through a conveyor belt 7, etc., then cut by a cutter 8, and stacked on a stacker 9. Therefore, it takes a lot of cost to equip the manufacturing facility and there are few companies capable of manufacturing the materials accordingly so that the manufacturing cost of the material is very high. Further, the cut glass fibers 2b can be broken or cut by heat and pressure in the extruder 5, and the length of the fiber (fiber length) is further shortened, whereby improvement of the properties thereof is not efficient. Here, the roving yarn refers to a bundle of fibers that are wound uniformly.
In addition, external noises, for example, fricatives between a tire and a ground, noise generated by high-temperature and high-pressure combustion gas flow in an exhaust system, noise which is generated in an engine and transmitted through a vehicle body or air (noise generated in the engine room), are introduced to the interior of the running vehicle through various paths, which hinders the feeling of quietness of the vehicle.
Therefore, it has been required to develop a material having excellent strength even in the winter season and excellent sound-absorption and heat-resistance.